This invention relates to a method for manufacturing a semiconductor device, and in particular to a method for manufacturing a semiconductor device where the formation of a thin film is involved.
An upper limit in temperature and the controlling of atmosphere in the process of manufacturing a semiconductor device are both important parameters influencing the quality of the resultant device. For example, although aluminum has been employed for a multilayer interconnection of an integrated circuit, the upper limit in processing temperature in subsequent to the formation of aluminum wirings is required to be set to 450 to 500.degree. C. or less, since the melting point of aluminum is relatively low. On the other hand, it is important that the metal oxides to be employed as an electrode material of high dielectric constant should be precisely controlled in composition. It is well known however that the metal oxides may be badly deteriorated in quality as they are exposed to an oxidizing atmosphere.
Meantime, as far as the formation of a thin film is concerned, various heat treatments and chemical reaction processes for modifying the characteristics of the thin film or for stabilizing the quality of the thin film should be positively employed. However, since various processes are successively performed on the surface of a substrate in the manufacture of a semiconductor device, a heat treatment or chemical treatment (such as an oxidizing treatment, a reducing treatment or an acid treatment) of a thin film formed on the substrate may cause a damage to the structure, etc. of underlying layers, so that it is frequently impossible to perform such treatments. Followings are typical examples of such a case.
When an aluminum multilayer interconnection is to be formed, an interlayer insulating film is interposed between the wiring layers for insulating the wiring layers from each other. This interlayer insulating film is required to be excellent in moisture resistance, in electrical insulating properties and in step-covering properties.
An SiO.sub.2 -based insulating film is commonly employed as this interlayer insulating film. An SiO.sub.2 -based insulating film of high quality is generally formed by means of a chemical vapor deposition method making use of a thermal reaction. For example, the insulating film may be formed employing tetraethoxy silane as a source gas at a reaction temperature of 650.degree. C. or more. However, when a substrate bearing an aluminum wiring layer thereon is subjected to such a high temperature treatment, the aluminum wiring layer may be melted away thus making the aluminum wiring layer incapable of functioning as a wiring.
In view of this problem, there has been tried to employ other energy means such as plasma excitation so as to lower the processing temperature. However, the process employing means such as plasma is accompanied with a problem that the resultant film may be contaminated with reaction products of various kinds. Furthermore, there is a problem that the quality of the resultant film may be greatly affected by a non-uniformity of plasma. Because of these reasons, an insulating film to be formed by means of a plasma excitation for instance is poor in quality as compared with an SiO.sub.2 -based insulating film to be obtained through a high temperature thermal decomposition. There has been also proposed, with a view to overcome this problem, to apply a heat treatment or an oxidizing treatment to an insulating film that has been formed by means of plasma excitation, etc. However, since the upper limit in temperature in such treatments is at most 450.degree. C., it is still impossible to obtain a sufficient effect.
As explained above, the application of a thermal treatment or a chemical treatment to a thin film is effective in providing the thin film formed on a semiconductor substrate with a desired property so as to obtain a thin film of high quality. However, since a heat treatment or chemical treatment of a thin film may cause a damage to other materials or structures of underlying layers, it has been frequently impossible to perform such treatments, thus making it difficult to form a thin film of high quality.